Giving Vitamin C, 500 mg. per day (the human kind is fine) can help acidify the urine and help dissolve crystals. Start him off at 100 mg if he is having diahrrea (sp?)
If it's bright red blood in the stool, there is usually some kind of irritation lower down in the bowel. Try feeding chicken and rice, or not feeding at all for 24 hours and see how it goes